pcalendar joins stuff

DB stuff

rails g scaffold user name:string
rails g scaffold prediction title:string
rails g scaffold position believes_it:boolean

rails g migration position_belongs_to_user
#class PositionBelongsToUser < ActiveRecord::Migration
#  def self.up
#    add_column :positions, :user_id, :integer
#  end
#
#  def self.down
#    remove_column :positions, :user_id
#  end
#end

rails g migration position_belongs_to_prediction
#class PositionBelongsToPrediction < ActiveRecord::Migration
#  def self.up
#    add_column :positions, :prediction_id, :integer
#  end
#
#  def self.down
#    remove_column :positions, :prediction_id
#  end
#end

rake db:migrate

IRB

ActiveRecord::Base.logger = Logger.new STDOUT

sully = User.create :name => 'Sully'
nick  = User.create :name => 'Nick'
pred1 = Prediction.create :title => 'something'
pred2 = Prediction.create :title => 'else'

# Sully and Nick believe in opposite predictions.
sully_pos1 = Position.create :believes_it => false, :user => sully, :prediction => pred1
sully_pos2 = Position.create :believes_it => true, :user => sully, :prediction => pred2
nick_pos1 = Position.create :believes_it => true, :user => nick, :prediction => pred1
nick_pos2 = Position.create :believes_it => false, :user => nick, :prediction => pred2

# Users who believe pred1.
User.joins(:positions).where('positions.believes_it' => true, 'positions.prediction_id' => pred1.id).to_a

position.rb

class Position < ActiveRecord::Base
  belongs_to :user
  belongs_to :prediction
end

prediction.rb

class Prediction < ActiveRecord::Base
  has_many :positions
  has_many :users, :through => :positions
end

user.rb

class User < ActiveRecord::Base
  has_many :positions
  has_many :predictions, :through => :positions
end